It is customary to produce flat glass as a continuous sheet, and to cut this continuous sheet into large glass sheet products. These large glass sheets are then commonly cut further to sizes needed for end products.
In the past, glass sheets were typically separated into smaller sheets by mechanically scoring the glass along an intended line of separation. The sheet was then bent underneath the scoreline to break the glass into separate sheets. This method produced a large number of glass chips, both during the scoring operation and when the glass sheet was bent and broken along the score line. For applications such as architectural and automotive glass which required relatively moderate dimensional and surface quality, such methods were sufficient.
However, glass sheets are now being utilized in applications which require higher dimensional and surface quality. One such application is flat panel displays, such as liquid crystal display (LCD) panels.
Various methods have been proposed to minimize the number of glass chips produced during glass breaking operations. In one method, the glass is mechanically scribed or abraded at the very edge of the glass sheet to form a crack initiation point. The crack is then drawn across the glass sheet using a laser along a desired line of separation. Such a process is further described, for example, in Patent Publication No. WO 93/20015, the specification of which is hereby incorporated by reference. The laser heats the glass, creating stresses within the glass sheet which cause the crack to propagate. By moving the laser, the crack is made to travel across the sheet. The laser can be used in conjunction with a water cooling stream or jet to improve this operation.
Such breaking processes can be achieved either with or without mechanical force to aid the breaking process. Because no mechanical scoring is utilized, the number of glass chips formed during the sheet breaking process is greatly reduced. In addition, the number of lateral cracks or flaws is also greatly reduced.
However, there is still a need to protect the glass sheets from water, dust, dirt, and any glass chips that are still inevitably formed during the glass breaking process. This is particularly true for glass sheets which are to be used in LCD and other flat panel displays. Glass sheets for LCD applications typically undergo further processing, after the breaking operations. This further processing requires as pristine a surface as possible.